Component oven



A ril 8, 1969 L. MARCOUX 3,437,790

COMPONENT OVEN L MARCOUX COMPONENT OVEN A ril 8 1969 L' MARCOUX COMPONENT OVEN A ril 8, 1969 L. MARCOUX COMPONENI dVEN Well as a heat insulation nlaterial conventiona1 in the art. 'Ihe insulation 16 vvill keep heat 10Sses of the Oven t a minimum The 1)ins 24 and 25 r0trude from potting material 1G as shown il1 FIG l and are Teceived in Inating clips 25 and 27 respectively The clips 2G and 27 are contained in bores 33 forn1ed in base 14, A conventional n10unting assembly 40 is attached to the b0ttom of the base 14 Which includes shank 4z f0rmed With key 44 Which serves to pr0perly orientate the oven for insertion in a receiving !Tleans (novv shown). 'I`le Inounting asseT1bly 40 1Tlounts pins l8. FI(.... 3 Shows a schen1atic Wiring diagran1 indicating the interna1 electrica1 connections of pins l'-8. Conductor 34 i()i11s pin l to cip 27 and hence the bott0l of PTC elenlent 18 via pin zs conductor Z8 and layer zz. (:0nductor 35 j0ints pin 3 t0 clip z6 and hence the top of 1 TC elenlent 18 via pin z4, conductors 30 and 32 and layer 2G' The cotnponents 50 (crystas, diodes, etc Which are to be n10unted in the oven cavity 11 are Inounted in Supports or S0ckets 46 and 48 (the num ber of Supports or Sockets provided iS optiona], tvv0 are shown for convenience) Pins 4 and 6 0f the mounting asseInbly 40 are connected t0 Socket 46 by conductors 3 and 37 re Spectively Pins z and 8 are connected to Socket 48 by conductors 38 and 3 Tespectively. Pin is grounded and 1)in 7 is not used 1/Ieta1 cap 12 encses the oven l(} and is atached t0 base 14 by any conventional Ineans, Such as screws 13.

Heating and regulating current (Ac or DC) is appHed through the PT( elenlent 18 from pin l t0 conductors 34 clip 27, pin z5, conductor z8, layer zz, through PT( element 18 layel 20, conductors 32 and 30, pin z4, clip z conductor 35 to pin 3. Elelnent 18 acts as a heater and also aS its ovvn tenTperature Tegulator' The current Passing through the l l( nateria1 causes heat to be generated thereby heating the oven cavity ll once the oven is Warmed up, it is noted that very little tenTperature variation 0ccus Within the cavity 11 Tegardless of an1bient tenperature uctuatiOnS 011tside the 0ven, i e., changes in heat deInand, Or appreciable uctuati0nS in '[he applied v01tage' A Telatively constant arnbient is pr0vided in the oven for the C0Inponents contained therein and this is achieved without moving parts and Without any elaborate, Conlparatively complex citcuitry T'he Telatively 10W heat generation of conponents Within the oven has been found to have a neg1igible eect in the inside temperanlre 0f the 0ven For the Successfu1 0peration of the 0Ven Within 'he pur- Vievv of the invention, the Se]f-regulating heating elenent 18 n1ust be constructed of Inaterial having as a characteristic a large 1)0Sitive teperature c0eicient of fesistance (PTC); that iS, material in Which the percent change in Tesistance pel degree change in temperature in the SO Called breakp0int range (about 230 F. 0n tl1e curve 0f FI(. 4) is very large, preferably ffom 30% to l0% per degfee centigrade 'Ihis break-p0int 1ange 0ccurs near the Curie or transiti0n point of the material and is sometimes referred to as the PTC anomal FIG. 4 shovvs the TesiStivity-temperatue curve c of Such a material vvhile I d0 not wish to be bound by any par ticular theory as to vvhy the oven operates aS it does, a 0Ssible explanation is as f0110vvs: ^'t ten1peratures above the anonla1y near p0int z7 0n Curve C very little heating 0ccurs since resistivity increases Inuch In0re ra1)idly than temperature at temperatures above the anomaly. Therefore heat generation, vvhich iS inversely proportiona1 t() l'e sistivity, dr0ps off drastically above the anonaly. IIeat transferred through regions of relatively high teIllerature Such aS Portions of elenlent 18 radially renoved fr01 the surface 17 iS acc0rdingly lov vvith the result that the tempefature gradient is als0 10w When the temperature in a Tegi01becomes depressed be10w the an0maly, section 0f curve Say by la :eduction of temperature along Sur face 17 the Tesulting drop in Tesistivity causes a gTeatly increas0d current 0W and attendant rate 0f heat geneTa tion in that region along the surface and thus a sharply increased gradient in those adj0ining regions that n1ust conduct the heat away AS the Surface ten1peratre is de Pressed further, the an0maly temperature n10ves radially inward toward the 10Igitudinal cylindrical axis creating regions of high heat generati01 aS it Passes through. Those regions at temperatures above the anonlaly continue to generate heat at approximate1y the sanle 10W rate and thus theif temperatures are hardly aected by such change in Surface tenperature.

In the emb0diment of FIG. 1 the greater part of the heat OW is perpendicular t0 the current HOW The heat flows radiauy in elexnent 18 While the current i lows axially. If the outside ten1perature decreases, ie', heat deinand is increased, thereby Teducing temperature of the outer Sllrface 17, the Tesis[ivity Of that Same area vvill a1so be Te duced. This Will cause an increase iIl current at the surface 17; hovvever, current throughout the main body of the elenent 18 Will renlain fairly constant IIeat generation at the surface vvill increase; this Will tend to OSet the teln perature reducti0n induced by increased heat denTand. IIence, th element vvill generate heat at the Surface 17 Where it is most useful.

The oven inherently operates in the range vvhich in cludes the an0[naly p0int, this is appr0ximately 230 F on the curve Shown in FI(... 4. The Inaterial, vhich ten1 peratureresistivity curve is Sh0wn, iS lanthanum doped barium titanate, the preparati0n of vvhich is described infra. ()rdinarily, the bariuIn titanate family of ceramics has an electrical fesistiVity of a Inagnitude greater than 10 0hm cm.; however, proper doping can Teduce the resistivity t0 less than 10 ohm cIn. Lanthanun1 doping of bariuIn titanate produces an exceptionally Steep slope of the reSistiVity-tefnperature curve at telT1peratures above the an0maly p0int combined With a elatiVely low base resistivity at tefnperatures be10w the anonlaly Point ()ther doping elements may be used to modify the anon]aly te n perature, the base Tesistivity and the rate of change ()f resistivity vvith temperature above the anomaly tempera ture AS an example, One Se1fregulating heater elel11e1t 18 WaS made using Ba la Ti() as fon0ws' The ravv Inaterials used -vere reagent grades of bariun1 carbonate (Ba(:0 lanthanum carbonate and titanium dioxide (Ti0 These were weighed out t0 an accuracy of about 25% 'O form st0ichi0Inetric mix' tures, plus 0.1 mole percent excess Ii0 in order to assure the formation of a liquid phase during nal ring These 111aterials were mixed and a sucient amount of distilled Water was added t0 form a 20% Solid mixture by Weight. This mixture was ball miued and dried '1he dried product vvas powdered and calcined in order to convert the Inate rial into the desired doped conlpound (Ba la '1^i() by firing at appr0xiInately 1,000 in ail and cooled 'lhe nateria1, in the form of a Porous cake, similar in tex tllre and appearance to Soft blackboard chalk, vvas broken up and vet milled as above, dried, con1minuted and Sieved fron 40 to Z70 (IJ(S, Standard sieves). Ihe resulting powder Was again immediate1y dried to drive 0ff any moisture vvhich might have been absorbed during com- Ininution and sieving and nally pressed into the desired cylindrical shape using conventional closed die ceraInicpressing techniques on a hydral11ic press. The Tesulting compacted powder body was fired tq the ceramic state at about l 500 C. Further details regarding the preparation of Similar PTC materia1 may be found in copending application, led Apr 13, 1964, Ser. No 3j9,3'70 assigned to the assignee of the instant invention.

Any material Which displays a relatively Steep positive S10ped reSiSitivity-temperature curve can be 11Sed as the heat generatingse1f reg[1lating elem6nt in accordance vith the present invention Such as the carbon black lled crosslinked 0lyethylene disc10sed in copending application of 5 Francis Buiting and Ioseph vaseleski, Ir`, Ser. 1Io. 472,108 filed july l 196, and assigned t the assignee of this invention.

FI(}. shovvs another embodiment of the invention It is inp0tant to achieve a hon10geneous heater ele111ent of constant de1sity S0 that the resistivity is consistent, i.e., internal cracks or n0nconducting inclusions 1Ill1st be avoided( The oven in 1 I(}' S lends itself t0 the achieve ment of Such uniformity by emp10ying a Stacked disc con figuration. The only dierenCe betvveen oven 10 0f FI( 1 and oven 1D0 Of FIG. j is the form of the 1 TC heater- Tegulator elenlent and electrical connection thereof. The description of the remainder of the device will, therefore, not be repeated.

The heater-Se1fregulat0 assembly 118 is comp0sed of a plurality of annular discs 106, the nunber of vhich is a matter of choice but Shown in FIG. as eight, are Sand wiched between discs l and 104] These discs are made of PTC material having the same characteristic of a steeppositive Slope resistivitytemperature curve at tenperatures above the anomaly p0int as that Inaterial used il1 cyl inder 18. A conductive layer is attached by conventional Ineans t() the faces ()f each of these discs, the layers shovvn in FIG. j numbered from 107llz. The evennumbered layers l08-ll0 are electrica11y connected to conductor 131 by conductors l'z0. (;onductor 131 is connected to pinlz5 Layer llz is electrically connected to pin 125 by conductor lzz. oddnumbered layers lu7l09 are connected t() conductor 130 by conductors lzl (:bnductor 130 is electrically connected to quickdisconnect pin lz4. Bottom layer lll is connected to clip lz by conductor 123. It Inay be seen that this provides a Stack of discs, electrically connected il1 parallel and that the greater part of the heat flovv is Tadial and therefore perpendicular to the current 0W' This 'Will provide even better te11]perature control than element l 8 because it will minimize the eectS of any loca1ized areas of nonuniforn1 density and hence vvill 1Tlake resistivity more consistent thfoughout the stacked assembly 118.

Bottom disc 104 is provided vith bores 115 t0 rovide Space for conductors 13, 137 and 138, 139 vvhich lead to sockets 14, 148 respcctively Cavity 150 may be pr0- vided in base 140, if desired, to give still more room for the conductors Conductors 134 and 135 connect clips 127 and 12G to pins l and 3 to complete the electrical connections il1 the Sane Inanner as described suEra in reference to conductors 34, 35 in FIG. 1.

Instead of empying conductive layers, Inetal tabs n^lay be inserted betvvee11the PT( discs to provide the electrical'c011necti011s therefor. It Should be noted that sepa- Tate voltage Sources could be supplied to the severa1 discs Qf equal or varying magnitude t0 rovide a desifed axial (emperature gradient if desired.

In FIGS 6 and 7 is shown an oven 200 vvhich is aT- ticularly useful vvith transist0rs Transistor 202 is shown vvith three leads z03, 204 and zs, although it is obvious that any number of leads would Come within the purview Flange 212 Of can 210 atbutts shoulder 222 forined in tubular casing Inen1ber zz0 0f a thern1ally and elect[ically insulating Inaterial, Such as a thermoplastic (e g', nylon) End 25 0f casing 220 haS an annular ange zz in Which are fornled S10ts 224. Transistor leads 203 204 and 205 are 10cated in s10ts 224 and are retained therein )y Shou1- 'ders 228] These S10ts are shown t0 be rectangular in shape but could be any other convneient shape, Such as elipti- (;al. I`he PTC heater regulator element 230 iS Ting-Shaped and fits c10sely around can 210. Iayers z32 and z34 0f Silver (I' Other conductive Inaterial Serve as tel=minal Surfaces on opp0site faces of elen1ent 230. Leads z3 and 238 are electricauy connected as by S01dering, t0 layers 232, 234 respectively The leadS, as shown, contact the layers throughout appr0xin1ately 360 thefeby insuring uniforn1 electrical Conductivity through elenlent 230. Electrically and thermany insulating 0tting c0mpound 240 0f a conventional type is infilled around elelnent 230. Shoulder 244 is forIned in end portion 225 0f casi] g zz0 Vvhich Seats diSc z4z, f0rlned of an electrical insulating material such as a resin impregnated fiberboard. Disc 242' iS rovided vvith S10ts 246 t0 pr0vide access for I I(; heater leads 236 and 238- Shoulder 244 is 1)0Siti0ned to provide a predetern1ined air gap 250 between disc 242 and can 210 and p0tting material 240 thereby resulting in a desired thern1al insulati( 1' Instead of relying on air gap 250 S0Ine other thern1al insulation could be used.

A cover member 260 is p0sitioned closely around casing zz0 and can be f0 med of the Same electically, thermauy insulating material as the casing, i.e', ny10n Cover 20 is provided vvith pr0jection 262 Which serves aS a con11)0- nent vvedge to maintain transistor z0z iirmly in n10unting can 210. Annular projection or vvedge z4 in cover 260 contacts leads 203 204 and 205 biasing theIn against hub zzl of casing 220' This construction Serves to minin1ize heat 10SS thfough leads 203, 204 and 205. That is it decreases the effective Size of the heat Sink of the transistor leads The transist0r 202' is in close thermal relation t0 heater 230 resulting in lre efncient contr01 It has been found I1Seful to apply a coating of a heat transfer c0mpound to the outer periphery Of Inounting can 210 such as a silicon compound T'l1is facilitates heat conductance frolT1 the PTC element 230 through mounting can 210 to transistor 202. one Such c0mpound available is (...E G641 Insulgrea8e. A c0ating of this heat transfel' compound Inay also be applied t0 the outer periphery of transistor z0z further facilitating heat oonductance fr0 l the PT( heater.

It vvill be noted that in this eInbodiment and in the ones described infra the con1ponent is in intin1ate thern]al contact with the PTC heaterregulator element' ()ven 300 Which iS particularly useful for diodes and the like, iS Shown in FIGS 8-10. A diode 310 is shown p0sitioned in oven 300 and has two leads 311 and 312 Which extend therefr0m through the walls of the oven. Oven 300 com rises a hollow tubulaT-Sha ed PTC heater element 320, Element 320 as Shown is octagonal in cross Section, although it is 0bvious that the nunlber of faces provided is a matter of ch0ice, r0viding Tectangular Casing 340 is generally cylindrical in shape and con1` posed of an electrically and thern1ally insulating ITlate rial Such as a ther1T10plastic resin. An aperture 342 iS l)ro vided in b()tt0 n1 vvall 344 0f the casing to pern1it passage Of lead 311] Diode Seating member 350 is telesc0pically received in the bore of PTC element 320 and tS cl0sely ^therein Member 350 is constructed of a good thermally conducting but electrically inSulating material, Such as anodized aluminum Before il1serting diode 310 in seating nlember 350 a coating 0f heat transfer c0mpound nlay be applied t0 the outer periphery of diode 310 and mem ber 3S0' AS explained supra, this Serves to facilitate heat conductance froIn the l l c heater element 320 through Seating nlen1ber 350 to the diode 310 and av0ids hot Spots and the like An electrically insulating vvasher 352' Overlies the outer end of PTC element 320 'and aso retains member 350 Within casing 340. TeTninal members 354 and 356 are welded t0 leads 358 and 36G a^s best Seen in FIG 9 and are Separated by electrically insulating ter Ininal separator 362' 'lerminal n1ember 354 is provided With two downwardly depending ngers 364 3 Which are in good electrical contact as by S01dering with layers 327 and 335 respectively, aS best Seen in FIG. 10. T'el' Ininal menber 356 is provided vvith downwardly depend ing nngers 368 and 370 Which are in gd electrical c0n tact aS by Soldering with layes 3z3 and 331 respectively The terminal nlen1bers and associated vvashers are cov ered by cap 372 Which iS provided vvith slots 374 in Which leads 358, 360 arecated and apefture 376 through Which diode lead 312 extends Cap 372 iS also constructed of electrically and thermally insulating Inaterial, e'g. nylon, and is provided With an annular rib 378 vvhich iS received in a Inating groove 346 in casing 340 FIGS 11 and 12 are cross Sections of two other PTC ting elements Which can be used in place of element Referfing rst to FIG 11 PTC element 380 iS com- 1)0Sed of tw0 halves 381, 38z Eectrically conductive layers 383 and 384 are attached in a conventional nlanner t0 0pposite faces of half 381 Whne layers 385 and 386 are attached to opp0site faces Of half 382' Lead 3s8 iS electrically connected to layers 383 and 386 Whne lead 360 iS electrically connected to layers 384 385. It Wiu be seen that current vvill pass from the outer layers 383 38 through the PTC halves 381, 382 to layers 384, 385 thereby causing the element 380 t0 generate heat in accordance vvith the Present invention FIG' 12 Shovvs another PTC heater assembly 387 use ful in the diode oven of FIGS. 810. Assefnbly 387 is c0fnposed of a plurality of PTC Slabs 388 enclosed by electricany and thermany insulating member 3l' The l 'IC Slabs 388 have 01]ter electrically conductive layers 3,z and inner elecTicaIly conductive layers 393 conventionally attached respective1y[heret0. Diode seating Inember 394 retains the Slabs in place and is C01Strlcted of Inaterial which is thermany conductive but electricaly in- Sulating, Similar t0 Inember 350, e.g., anodized aluinum. A Silicone heat transfer C0Inpound may be applied to the outer surfaces of element 34 to enhance the thernal conductivity frorn the heating 1 TC slabs 388. Lead 3S8 is electrically attached to outer layers 392 and lead 360 iS electrically attached to inner layers 393 t0 eect a passage 0f current fl0m the outer layers 3z t0 the inner layers 33 It will thus be seen that the embodiments of the present invention 0fer numel`ous advantages over the prior art. Among them are for exan1ple lovv cost; Inininal iZe; Solid State control with no moving parts; Self[egulation I]Sing 10 1T10Ving Contacts, sensing circuits, anlplification circuits, etc'; extreIne simplicity; and ease 0f fabfication In vievv of the above, it Will be seen that the Several* 0bjects of the invention are achieved and other advantageous results attained.

AS various changes could be made in the above constructions and Tnethods without departing froln the Scope 0f the invention, it is intended that all Inatter contained in the above description or Shown in the acc0fnpanying drawing Shall be interpreted as illustrative and n0t in a linliting sense Also, it is to be understood that the phrase- 010gy or termin010gy emp10yed herein is fOT the purpose 0f description and not of limitation.

I claim:

- 1- A Se1f-Tegulating component oven c0nprising;

(a) an electrically and thermally insulating casing hav ing a bptt0m wall and upstanding vvall portions eX- tending thereffofn and forming an open ended casing yvith a cavity therein;

(b) lib members attached to Said upstanding wan ortions;

(c) a polygonal Solid state PTC element With a longitudina1 axis and having a plurality of axial faces 10cated in said Cavity and having a coaxial bore;

(d) electrically conductive layefs attached to alternate Said faces;

(e) two terminal members With depending ngerS Sep arated f0n each other by elect[ical insulation Inounted on the 0pen end of said casing, the fingers of Said terminals being electrically connect d to Said layers attached t0 said faces;

(f) said rib members contacting at least some 0f the axial faces having no electrically conductive layer attached thereto; component Seating member telescopically received (g) an electrically insulating, thermany conducting component Seating member telescopically received in close thermal relation in the bore of said PTC element;

(h) heat tra11sfer coating applied t0 the outer periphery of said Seating member;

(i) electrical conductors ee1ctrically Connected t0 said terminal members;

(j) an electrically insulating cap member enclosing said open ended casing; and

(k) said cap mmeber, Seating member and bottom wan each provided With an apefture t0 provide access for the colnponent leads' z A Selfregulating COInponent oven comprising:

(a) an electrically and thern^lally insulating casing having a b0ttom vvall and upstanding wall 0rtions depending therefronl and forming an open ended casig with a cavity therein;

(b) a solid state heater leInent having a Steep Slope I T( temperatureeSiStivity curve located in said cavity and having a bore therein;

(c) terminal IeInberS attached to Spaced I0rtions of said PTC element;

(d) an electrical insulating cap menber enclosing said open ended casing; and Said cap member and bottom Wall each provided With an aperture to rovide acce'ss for electrical leads 3. An oven according t0 claim 2 including;

(e) rib members attached to said upstanding wan portions, Said rib Inembers centering Said P1'(: eleIlent; and

(f) an electrically insulating, thermany conducting C0T110nent seating meInber telesc0picaly Teceived in close therlnal reation to the bore of Said P1C element.

4' AI oven according t0 clain 3 Wherein Said l l element is generauy cylindrical and Said bore is coaxia, Said P'I`C element is Split axially into at least tw0 portions and (g) Said terminal members a e attached t0 two opposite 10I1gitudinal Sides of each Said portion s AI1 0Ven according to claim 3 Wherein said PT( element is c0mp0sed of a plurality of PTC Slabs arranged to denne said bore, Said terminals electrically attached t0 tvv0 0pposite faces 0f each said Slab,

A component oven c0mprising:

(a) an electrically and thermany insulating casing Inember, Said casing generally annular and having a d0wnstanding wall portion depending from a hub 1)0rtion, a Seating Hange forned between` said vau portion and said hub portion;

(b) an electrically insulating and therfnally conducting cup-Shaped component Seatifg Inember formed With a nge COInplementary in shape to said Seating ange and seated thereagainst;

(c) heat transfer COInpound applied to the outer periphery of said seating member;

(d) an annular solid state PTC elenlent closely tting about the periphery 0f said Seating member;

(e) electricany conductive layers on opp0site radial faces 0f said element;

(f) a Wire like terminal electrically connected 0 each of said layers throughout approximately 360 there- 0f each Said terminal extending beyond Said casing member;

(g) electricauy insulating potting material mmled around Said PTC element between Said casing member and said Seating member;

(h) a Tecessed portion formed in the ffee end of' Said downstandin wall portion and spaced axially frm Said Seating member toward Said free end;

(i) an electricauy insulating disc member Seated in Said recessed portion, Said disc member having apertures therein through Which sai(1terminals extend;

(j) Component lead gr00ves located on the outer surface of said casing member and extending axiauy theret0, Said grooves having a Seating pOfiOn and an ingress ))rti()n, Said ingress portion narrowcr than Said seating porti01; and

(k) an electrically insulating cup-Shaped cover nlember closely fitting over said casing member, Said cover n1ember having component lead vvedge means adapted t0 bias the component leads against Said hub 0f said casing, said cover Inember also havingcon1- ponent wedge nleans adapted to Secure a component in Said c0nponent seating Inen1ber.

7' A c0mponent oven c0mpriSing (a) an electricauy and thermally insulating casing having tW0 ends;

(b) a Seating lange formed in one end Of Said casing;

(c) an electrically insulating and thermally conducting con1ponent Seating n1enTber l0cated Within Said caS ing With a ange complementary in Shape to Said seating ange and Seated thereagainst;

(d) a S0lid State heater elen1ent having a Steep S10pe )0sitive teInperature-resistivity curve placed about the eriphery Of said con1ponent Seating Ineinber in close thermal relation theret0;

(e) terninals electrically attached to Spaced OTti011s of Said heater eleInent;

10 (f) an electrically and thermal]y insulating men1ber C10Sing the 0ther end of Said casing; and

(g) an electrically and thernlally insulating COVer meInber closing Said one end of Said casing( 8. A component oven acc0rding t0 Clain1 7 in Which said casing has c0nponent lead gr00ves extending in a direction funning from said one end to Said Oher end and Said cover Inember adapted to bia8 Said c0mponent leads against Said casing thereby limiting the heat sink eect of said leads' A con]ponent oven according t0 claim in Which Said PTC element material is Ba Ia Ti0 10- A C0Inponent oven according t0 claim in vvhich Said P1( element Inaterial is a carbon black filled crosslinked polymer ll A c0nlpOnnt oven according t0 claim 1 in which Said PTC element I11aterial is Ba Ia '1 i() 12- A c0mponent oven according to clain1 1 in Which said PTC element materia1 is a carbon black filled crosslinked p01ymer References cited UNITED STATES PATENTS 4/1960 Schusterius Z19Oj x 6/1962 vv0lfskill 219 210 

